This invention relates to an apparatus for measuring the temperature of a wafer and more particularly to an apparatus for measuring the temperature of a wafer by a non-contact method.
Both direct and indirect methods have been in use for measuring the temperature of a wafer. By the direct method it is meant a method whereby a sensor is brought into direct contact with the target wafer. When a sensor is thus brought into contact with the wafer, however, the contact itself tends to cause a change in the wafer temperature, thereby adversely affecting the accuracy of the measurement. Another disadvantage of direct measurements is that the wafer may be more easily contaminated by the contact. As for the indirect methods, on the other hand, the accuracy of measurement cannot be expected to be high since what is actually measured is the temperature of some other medium which is in contact with the target wafer. When there is a sudden change in the wafer temperature, furthermore, there is bound to be a time delay before such a change can be detected. This also adversely affects the accuracy of the measurement.